This invention relates in general to vehicle brake systems and in particular to an anti-lock brake system.
An anti-lock brake system is often included as standard equipment on new vehicles. When actuated, the anti-lock brake system is operative to control the operation of some or all of the vehicle wheel brakes. A typical anti-lock brake system includes a plurality of normally open and normally closed solenoid valves which are mounted within a control valve body and connected to the vehicle hydraulic brake system. Usually, a separate hydraulic source, such as a motor driven pump, is included in the anti-lock brake system for reapplying hydraulic pressure to the controlled wheel brakes during an anti-lock brake system braking cycle.
An anti-lock brake system further includes an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, a plurality of solenoid coils associated with the solenoid valves and wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The control module is typically mounted upon the control valve body to form a compact unit.
During vehicle operation, the microprocessor in the anti-lock brake system control module continuously receives speed signals from the wheel speed sensors. The microprocessor monitors the wheel speed signals for a potential wheel lock-up condition. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor and selectively operate the solenoid valves in the control unit to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.